Trying to mount an ext2 / ext3 / ext4 device using external drivers on OSX might bring up the following error:
disk media is not present
To fix that a virtual machine helped.
Attaching the external drive using usb, creating a filter for that usb device to forward it to the ubuntu based VM.
to find the right device.
Now go with fsck.ext3 (for ext3 only)
fsck -y /dev/sdd
-y means answer every question with yes.
For a 2 TB HDD that might take up to several hours, but after that is finished, you can try to mount the drive again.